The present invention relates to a dispenser for fluids, and to a method of manufacturing it.
To dispense small predetermined quantities ("doses") of fluid, in particular semisolid substances such as pastes or creams, it is known to make use of manually-actuated pumps of the kind to be found in sprays, and more particularly precompression pumps. European patent EP-0-251 863 filed in 1987 by Valois teaches associating such a pump with a deformable tank of the substance, e.g. a tube made of plastics material. If the pump is mounted in sealed manner on the tank, it is possible to empty practically all of the contents from the tank. Whenever a dose is expelled by actuating the pump, the tube is flattened correspondingly under the combined effects of atmospheric pressure on the outside of the deformable tank and the suction created by the pump inside the deformable tank.
That type of dispenser has other advantages. In particular, the substance in the tank can be conserved without coming into contact with air, thereby avoiding any risk of it being oxidized or contaminated. In addition, the dispenser works regardless of its position relative to the vertical.
However, when the tank is partially empty, the tube takes up a flattened form that is difficult to hold in the hand. Actuating the pump by pressing a finger on the dispenser head becomes awkward.
Provision could be made to dispose a more rigid envelope around the deformable tank so that the dispenser keeps a constant outside shape, as in double-envelope dispensers such as those described in U.S. Pat. No. 4,322,020 filed in 1980 by Stone. Unfortunately, such dispensers are relatively difficult to manufacture.
Dispensers are also known that have a double-walled tank with a flexible inner wall and a rigid outer wall, which tanks are made by blow coextrusion of the two walls, and welding by simultaneously pinching the ends of the two walls, the welding of the rigid outer wall being porus or permeable so as to enable air to penetrate between the two walls. Such a dispenser must be made using a method that is very difficult to master since the two walls must avoid welding together during blowing, and the weld at the end of the outer wall must leak while the weld at the end of the inner wall must be sealed. In addition, the materials that can be used for the inner and outer walls are very limited. Finally, the coextrusion method generally requires air to be blown between the two walls after they have been formed in order to separate them: this increases the cost of implementing the method.